Abstract

The specification for enhanced mail system status codes, RFC 3463,
establishes a new code model and lists a collection of status codes.
While it anticipated that more codes would be added over time, it did
not provide an explicit mechanism for registering and tracking those
codes. This document specifies an IANA registry for mail system
enhanced status codes, and initializes that registry with the codes
so far established in published standards-track documents, as well as
other codes that have become established in the industry. This document
specifies an Internet Best Current Practices for the
Internet Community, and requests discussion and suggestions for
improvements.